Preliminary results of size distribution airborne particles in Mexico City

Particulate matter concentrations were measured in five size ranges, during an annual period, at the National University Campus in Mexico City. Size distribution indicated high particulates values in the size ranges from 3.0 to >7.2 μm and from 0.49 to 1.5 μm. The cascade impactor concentration represented 30% of the total suspended particles (TSP) values, with a correlation of 0.6 between them. No significative seasonal difference in the mass paniculate size distrubition was found, but in the rainy season a slight increase in fine particles with respect to the total mass impactor was found. The application of a respiratory model showed that maximum mass of coarse particulates deposition in the thoracic region was of 27 μg hr^?1. The highest concentration of fine particulates deposition reached only 13 μg hr^?1, in activity.     

Preparation and Characterization of Starch Particles for Use in Pickering Emulsions

Particle‐stabilized emulsions, called Pickering emulsions, can be produced by using starch particles. In this work we studied how the properties of the starch particles affect the droplet size and creaming of such emulsions. In the study, various sizes of starch particles were generated by two different methods and used to stabilize Pickering emulsions. Sedimentation according to Stokes’ law was used to separate small and large starch granules. Acid hydrolysis was another method used to obtain smaller particles. All samples were modified with octenyl succinic anhydride (OSA) to increase their hydrophobicity with a level of OSA substitution between 1.8 and 3.1%. The size of starch particles was the main factor influencing emulsion droplet sizes. Furthermore, the droplet size decreased as the starch concentration increased. Using small starch particles with sizes <10 μm produced stable emulsions with smaller droplet size compared with larger sizes of starch particles, >10 μm. When subjected to acid hydrolysis, smaller starch particles were generally obtained, which could subsequently create smaller emulsion droplets. The emulsion index increased for the acid‐hydrolyzed starch owing to the size reduction of starch particles. The shape of the starch seemed to have a minor impact on the droplet size and the creaming of Pickering emulsions.     

Controlled release of the herbicide norflurazon into water from ethylcellulose formulations

The herbicide norflurazon was encapsulated in ethylcellulose (EC(40)) microspheres by the solvent evaporation technique to obtain controlled release formulations. The kinetics of release of the active ingredient into the aqueous solution from different preparations was determined. It was found that the percentage release of the incorporated herbicide was a function of the composition and formation conditions of the formulations (amount of emulsifying agent, EC(40)/herbicide ratio, stirring speed, and percentage of pore-forming agent). The percentage of the herbicide release was related to the properties of the different microspheres obtained, such as particle size distribution, herbicide loading, or surface morphology. The release percentage depended inversely on the particle size of the microspheres and directly on the content of active ingredient and emulsifying and pore-forming agents. An empirical equation was used to fit the herbicide release data, indicating that the release of norflurazon from the various formulations is controlled by a diffusion mechanism. The time taken for 50% of the active ingredient to be released into water (T(50)) was calculated, showing a wide variation among the different preparations (0.95-16.4 days).     

延长黄原胶缓释期的技术研究

【目的】研究了水杨酸(SA)在黄原胶(XG)及聚乙烯醇(PVA)为主要材料的基质型缓释系统中的释放速率。【方法】共设计了29个配方,分为4组:XG + PVA + SA、XG + PVA + 醋酸酯淀粉(AS) + SA、XG + PVA + 硬脂酸 + SA、XG + PVA + 壳聚糖(CS) + SA。根据设计的配方将材料研磨混匀后以聚乙烯醇溶液为粘合剂进行造粒。首先制作了6～10 mm五种造粒直径的缓释颗粒,并以4%、5%、6% (w/v)三种浓度的PVA溶液分别造粒,研究了造粒大小、PVA溶液浓度对颗粒释放行为的影响。确定造粒条件后研究了四种配方不同配比对颗粒释放行为的影响,采用静水溶出法和土柱淋溶法对释放行为进行表征,以水杨酸的释放率及累积释放量为指标绘制释放曲线。【结果】所制缓释颗粒的水杨酸释放曲线都遵循一个趋势:水杨酸释放率在前一段时间呈快速增长,转折点之后增长速度趋于平缓。根据试验结果分析,粗粒径的黄原胶溶胀更缓慢,对内容物的释放也会更慢。缓释颗粒直径较小时最终释放的百分比更高但由于比表面积大释放也更快,颗粒直径过大时最终释放的百分比会降低且持续时间也不会延长,最终选定造粒直径8 mm。对粘合剂PVA溶液的使用量的研究结果显示,在选取的三种PVA溶液浓度中,以浓度为4%的PVA溶液进行造粒、混合粉末与4%PVA溶液的比例(w/w)以1.1∶1为宜。四种不同组成的配方经优化后缓释效果最好的比例分别为:XG∶SA = 3∶1,在去离子水中释放持续约2.5天;XG∶AS∶SA = 3∶1∶1,在去离子水中释放持续时间2.5天;XG∶硬脂酸∶SA = 1∶1∶1,去离子水中持续时间约为3天;XG∶CS∶SA = 3∶1∶1,在去离子水中可持续4天,而在土柱中释放持续可达36天左右。【结论】使用0.178 mm粒径的黄原胶粉末,在XG∶CS∶SA = 3∶1∶1,造粒直径8 mm,以4% PVA溶液进行粘合造粒的条件下,所得缓释颗粒的土柱淋溶释放时间可长达36天,为本试验所得释放时间最长的缓释体系。该缓释系统成本较低廉,制作方法简单,对环境友好。     

旋风除尘器对生物炭粉的除尘特性

生物炭粉是生物质热解液化工艺的主要副产品之一,其被清除的效果对生物油质量有较大影响。该文以下降管式生物质热解液化装置作为试验平台,试验分析了旋风除尘器对炭粉的除尘效果。该工艺中,进入旋风除尘器的热解气含尘浓度范围一般为35～50g/m3,且浓度随机波动较大;旋风除尘器收集的炭粉粒径范围为0.39～30μm的颗粒占总量的91.29%,几乎没有小于0.39μm和大于40.72μm的颗粒;旋风除尘器的除尘效率不高,一般低于80%。旋风除尘器的除尘效率随热解气中炭粉浓度增加而略有提高。     

The kinetics of extraction of soil-applied metoxuron by methanol and its biological implications

The effect of three levels of moisture (saturation, field capacity, 50% field capacity) and two temperatures (10 and 27 °C) on the extraction of sil applied metoxuron by methanol was determined for an alfisol and a vertisol. Technical grade metoxuron applied at 20 μg g^?1 of soil, was extracted by shaking with methanol for 30 min and assayed spectrophotometrically after correcting for soil blanks. There was an initial steep fall in the extractable portion for about 40 to 60 days followed by a much slower decrease in all the cases upto 150 days. The time of 50% extractability of the added herbicide (t₅₀) was lower at 27 °C than at 10 °C, the difference being more marked for the alfisol. The effect of moisture which varied from 40 to 10% for vertisol and 30 to 7.5% for alfisol was not significant. The specific rate of decrease of extractable metoxuron was similar at both temperaturs for the vertisol, and was significantly lower for the alfisol at 10 °C. The observed pattern of the kinetics of methanol available metoxuron is interpeted in terms of an initial rapid partitioning of the herbicide into labile and nonlabile compartments followed by a probable slow release and degradation path. The specific reaction rates for the different steps have been estimated and correlated with other soil properties and their implication on the bioavailability of the herbicide by considering methanol extractability as a suitable index is discussed.     

Faster fermentation of cooked carrot cell clusters compared to cell wall fragments in vitro by porcine feces

Plant cell walls are the major structural component of fruits and vegetables, which break down to cell wall particles during ingestion (oral mastication) or food processing. The major health-promoting effect of cell walls occurs when they reach the colon and are fermented by the gut microbiota. In this study, the fermentation kinetics of carrot cell wall particle dispersions with different particle size and microstructure were investigated in vitro using porcine feces. The cumulative gas production and short-chain fatty acids (SCFAs) produced were measured at time intervals up to 48 h. The results show that larger cell clusters with an average particle size (d(0.5)) of 298 and 137 μm were more rapidly fermented and produced more SCFAs and gas than smaller single cells (75 μm) or cell fragments (50 μm), particularly between 8 and 20 h. Confocal microscopy suggests that the junctions between cells provides an environment that promotes bacterial growth, outweighing the greater specific surface area of smaller particles as a driver for more rapid fermentation. The study demonstrates that it may be possible, by controlling the size of cell wall particles, to design plant-based foods for fiber delivery and promotion of colon fermentation to maximize the potential for human health.     

Size Distribution of Trace Elements and Major Ions in the Eastern Mediterranean Atmosphere

Size distribution of trace elements is measured at the Mediterranean coast of Turkey, by analyzing hi-vol impactor samples collected between August 1993 and May 1994. Mass median diameters of marine elements are between 4.6 and 5.3 μm, and those of crustal elements are between 3.0 and 3.5 μm. Mass median diameters of crustal elements are 30% smaller in samples impacted by Saharan Dust. Pollution derived elements, As, Cd, Mo, Pb, Se, and Zn have MMD's between 1.25 and 1.01 μm. Although 70–90% of the masses of these elements were associated with particles smaller than 2.1 μm, 10–30% of their mass was associated with coarse particles. Coarse component in concentrations of Cd, Pb, Sb and particulate Hg are due to adsorption of fine anthropogenic particles on coarse crustal aerosol, whereas coarse fraction Zn, As, Se, In, Mo and Au are crustal at Al concentrations > 100 ng m^?3. Bromine, Cr, Ni, and V have bimodal distributions. The fine component, which account for approximately 30–40% of their masses are due to anthropogenic sources, whereas the coarse component, which accounts for 30–50% of their masses are due to sea salt for Br, and crustal particles for Cr, Ni, and V.     

日光温室土墙体温度变化及蓄热放热特点

为研究日光温室土墙体温度变化规律及蓄放热特性,以泰安市下挖式土墙日光温室为研究对象,在温室北墙布置5个测试层,通过各测试层最冷季节(30 d)温室内气温、墙体温度、室外气温及室外太阳辐照度测试数据,分析了土墙日光温室内部温度及墙体内温度的分布规律。结果表明:各测试层墙体表面及0.1~0.6 m处测点的温度均呈现出随温室气温周期性变化的规律,且随着墙体厚度的增加温度的波动幅值逐渐减小,相位明显后移;0.7 m以后测点的温度幅值趋于稳定,处于稳态向室外的导热过程。基于墙体温度分布规律,对墙体白天的蓄热量、夜间的放热量及墙体夜间放热效率进行了计算,得出墙体夜间放热效率为43%,表明土墙白天蓄积热量的43%用于改善夜间温室内热环境。对墙体蓄热和放热量计算,综合评价墙体的平均放热效率,可以为土墙日光温室结构优化及热负荷计算提供指导,为各地土墙温室轻简化技术研究提供理论基础。     

Concentration and size distribution of airborne particles in a broiler house

Airborne dust particles were sampled in a broiler house using the quartz crystal microbalance cascade impactor designed for the measurement of mass concentration and size distribution from 0.05 to 25 gm. No significant difference was noticed in the dust concentration from morning to evening or at different sampling sites in the broiler house. The concentration of airborne dust particles decreased as the age of the chickens increased. Ratio of dust particles smaller than 0.8 pm to the total dust ranged from 10 to 50%. The highest concentration of dust was in the particle size range of 3.2 μm. The fogging system in use reduced the concentration of larger particles but not that of the smaller particles.     

Paste Particle and Bean Size as Related to Sweetened Azuki Paste Quality

Influences of the amount of sugar, particle size of unsweetened paste, and bean size on sweetened paste quality were evaluated in two types of azuki. Increased sugar resulted in darker, less red, and less yellow sweetened paste and decreased hardness, adhesiveness, and chewiness of sweetened paste. Sweetened paste produced from larger particles was less red and less yellow than that from smaller ones. Paste particle size, as determined by sedimentation tests, was correlated with graininess of sweetened paste (r = 0.930**), indicating that the larger the paste particle, the grainier the sweetened paste produced. Protein content ranged from 22.3% in small beans to 26.1% in large beans in Azuki cv. Erimo and from 22.4% in medium size beans to 23.5% in large beans in Azuki WSU 262. Proportion of unsweetened paste particles that were <106 μm was 71.5% in small beans but only 39.3% in large beans in Erimo, and 38.7% in medium size beans, and 23.8% in large beans in WSU 262. Sweetened paste produced from larger beans was less red and lower in hardness, adhesiveness, and chewiness than that from smaller beans.     

Run-off transport of herbicides during natural and simulated rainfall and its reduction by vegetated filter strips

The efficiency of filter strips in protecting watercourses against herbicides in run‐off was evaluated in field experiments in western Germany. Surface run‐off caused by natural rainfall and related transport of metolachlor, terbuthylazine and pendimethalin were measured on plots of 40 m length without filter strips (F0), and after passing over three types of herbicide‐untreated field margin: 12 m conservation headland (CH12), 6 m (GF6) and 12 m grass strips (GF12). Run‐off was also measured after simulated rainfall on 7 m long plots without (F0) and with 3 m grass strips (GF3). All three herbicides were transported both in dissolved and in adsorbed forms; the partitioning depended on their water solubility with metolachlor and terbuthylazine mainly translocated in dissolved form (F0: highest mean concentrations for a natural run‐off event 721 and 220 μg L^?1, respectively). Pendimethalin was predominantly transported in adsorbed form (maximum mean concentration 11.2 μg L^?1). In the sediment, the highest mean herbicide contents in a single natural event (F0) accounted for 2294 μg kg^?1 (metolachlor), 1317 μg kg^?1 (terbuthylazine) and 5648 μg kg^?1 (pendimethalin). The proportions of applied herbicide translocated were 0.3% (metolachlor), 0.2% (terbuthylazine) and 0.06% (pendimethalin; F0, natural rainfall). The extent of herbicide transport decreased with time but within this trend soil sealing, soil moisture and amount and intensity of rainfall increased losses. Compared with the F0 plots, the reduction of herbicide translocation after natural rainfall reached 80–83% (CH12), 80–88% (GF6) and >99% (GF12) over the 3‐year period. The 12 m grass strips allowed only one extreme run‐off event to pass through, thus providing a highly effective watercourse protection against herbicide pollution.     

Significance of Wheat Flour Particle Size on Sponge Cake Baking Quality

We evaluated the effect and magnitude of flour particle size on sponge cake (SC) baking quality. Two different sets of wheat flours, including flours of reduced particle size obtained by regrinding and flour fractions of different particle size separated by sieving, were tested for batter properties and SC baking quality. The proportion of small particles (<55 μm) of flour was increased by 11.6–26.9% by regrinding. Despite the increased sodium carbonate solvent retention capacity, which was probably a result of the increased starch damage and particle size reduction, reground flour exhibited little change in density and viscosity of flour‐water batter and produced SC of improved volume by 0.8–15.0%. The volume of SC baked from flour fractions of small (<55 μm), intermediate (55–88 μm), and large (>88 μm) particles of soft and club wheat was in the range of 1,353–1,450, 1,040–1,195, and 955–1,130 mL, respectively. Even with comparable or higher protein content, flour fractions of intermediate particle size produced larger volume of SC than flour fractions of large particle size. The flour fractions of small particle size in soft white and club wheat exhibited lower flour‐water batter density (102.6–105.9 g/100 mL) than did those of large and intermediate particle fractions (105.2–108.2 g/100 mL). The viscosity of flour‐water batter was lowest in flour fractions of small particle size, higher in intermediate particles, and highest in large particles. Flour particle size exerted a considerable influence on batter density and viscosity and subsequently on SC volume and crumb structure. Fine particle size of flour overpowered the negative effects of elevated starch damage, water absorption, and protein content in SC baking.     

Sulfentrazone adsorbed on micelle-montmorillonite complexes for slow release in soil

Interactions of the herbicide sulfentrazone with the cationic surfactants octadecyltrimethylammonium (ODTMA), hexadecyltrimethylammonium (HDTMA), and benzyldimethylhexadecylammonium (BDMHDA) have been studied for the design of slow-release formulations based on sulfentrazone adsorbed on a micelle-montmorillonite complex. Adsorbed amounts of sulfentrazone on ODTMA- and BDMHDA-montmorillonite complexes were 99.2-99.8% of that added, and desorption of herbicide in water during 24 h was low. After 10 washings in funnels with soil, only 2.6% of herbicide was released from ODTMA-montmorillonite formulations versus 100% release from the commercial formulation. The strong binding of sulfentrazone to micelles was confirmed by pH and spectroscopic measurements and was explained by the formation of ionic pairs between cationic surfactant and anionic herbicide. The ODTMA-clay and commercial formulations of sulfentrazone yield almost complete and 40% growth inhibition of green foxtail, respectively, at 700 g of active ingredient/ha. Hence, the slow release from micelle-clay formulations of sulfentrazone promotes its biological activity and reduces environmental contamination.     

Soil microaggregation as influenced by uncharged organic conditioners

Abstract

To assess the interaction of water soluble stabilizing agents with soil particles, soil microaggregation was studied after treatments with two uncharged organic conditioners, Polyvinyl alcohols (PVAs) and Dextrans, of different molecular weight. The size distribution of microaggregates (diameter <250 pm) was determined on two soils of low organic matter contents with differing texture by means of a laser light technique. PVAs and Dextrans modified the microaggregate size distribution, increasing the proportion of >75 μm aggregates. The extent of this modification increased with the molecular weight of the conditioners and, for the same molecular weight, decreased with increasing amount of conditioner used. The aggregating effect of PVAs was stronger on particles smaller then 5 μm, which formed microaggregates in the range 10–100 μm which were not broken down even by ultrasonication. S.E.M. micrographs of soil aggregates confirmed the results reported above. PVAs and Dextrans appeared to produce a more porus structure with more aggregates of about 100 μm size, both in the clay soil and, to a lesser extent, in the sandy soil.     

Inorganic and organic clays as carriers for controlled release of the herbicide hexazinone

The risk of ground water contamination resulting from rapid leaching of highly soluble pesticides can be minimized through the application of the pesticide adsorbed on a matrix or carrier, which limits the amount of pesticide immediately available for undesirable losses. The use of natural materials for this purpose is of special interest in terms of economy and sustainability. In this work the adsorption of the herbicide hexazinone by two montmorillonites saturated with various inorganic and organic cations was determined and the ability of the two clays displaying the highest adsorption capacities [Fe(3+)-saturated Wyoming montmorillonite, (Fe-SW) and hexadecyltrimethylammonium-saturated Arizona montmorillonite (HDTMA-SA)] to act as carriers for slow release of hexazinone and to reduce herbicide leaching losses was evaluated. Hexazinone formulations based on Fe-SW and HDTMA-SA displayed slow release properties in water and soil/water suspensions, reduced herbicide leaching in soil columns, and maintained herbicidal activity, as compared with the currently available commercial hexazinone formulation (wettable powder). Loosely bound hexazinone-HDTMASA formulations, which led to the slowest breakthrough of hexazinone in soil columns along with the greatest amounts of herbicide released from the clay particles, displayed the most interesting characteristics for their use as slow release formulations and to prevent ground water contamination.     

Size Distributions and Concentrations of Spheroidal Carbonaceous Fly-Ash Particles (SCPs) in Lake Sediments as an Aid to Detecting Locally Deposited Atmospheric Pollution

Size distributions and concentrations of spheroidal carbonaceous fly-ash particles (SCPs) > 5 μm have been counted in surface sediments from 20 lakes along a 62 km west-east transect in the Bergen area, Norway. Increased concentrations of SCPs are found in lakes immediately downwind, closest to the city. These lakes also have a dominance of larger particles (> 10 μm) than further downwind where smaller particles (5–10 μm) dominate. The pattern of SCPs > 5 μm is compared with a previous study of anthropogenic Pb and SCPs > 3 μm in the same sediments. Along the transect there is a difference in pattern between the concentrations of SCPs > 5 μm and the patterns of anthropogenic Pb and SCPs > 3 μm. The result indicates that increased altitude and rainfall probably explain the increased concentrations of anthropogenic Pb and SCPs > 3μm in the eastern part of the transect. Metals are in the size range for which atmospheric residence times are greatest, whereas particles > 5 μm in diameter are of the size thought to be effectively removed from the atmosphere by sedimentation. This may explain, at least partially, why there is a difference between the pattern of SCPs > 5 μm concentrations and anthropogenic Pb and SCPs > 3 μm concentrations. This study shows that SCPs > 5 μm in lake sediments can potentially provide a better signal of locally-deposited atmospheric pollution than trace elements from the same source. A SCP distribution dominated by large particles (> 10 μm) is found up to 20 km downwind of the city. Within this area, temporal SCP size distribution patterns can help detect local-deposited atmospheric pollution.     

戈壁地表土壤颗粒的空间变异特征研究

研究戈壁地表土壤颗粒粒度特征及空间变异可为戈壁地区风蚀监测、评价及制定科学的防沙治沙对策提供参考。以吉兰泰盐湖西北部的堆积型细砾质戈壁为研究对象,基于数字图像技术计算了地表不同粒级颗粒的质量分数,并分析了颗粒空间变异特征。结果表明,图像处理技术提取戈壁地表土壤颗粒的效果较好,3个粒级颗粒质量分数总和为93.12%,粒径0.84 mm、0.84～0.42 mm和0.42 mm颗粒质量分数分别为69.81%、14.99%和8.32%,变异系数分别为14.12%、40.02%和55.06%,变异函数模型分别为高斯模型、高斯模型和指数模型,空间异质性尺度分别为632、691和1 875 m。3个粒级颗粒均呈斑块状分布,且C/(C_0+C)介于72.79%～79.37%,说明结构因素和随机因素共同影响戈壁地表颗粒的空间分布格局,但结构性因素(戈壁形成过程、地势、风蚀及植被分布格局等)是造成颗粒分布格局差异的主要驱动力。     

Effect of the herbicide fluazifop-butyl on fungal populations and activity in soil

The side effects of fluazifop-butyl on soil fungal populations and oxygen uptake were studied by incubating soil samples with a range of fluazifop-butyl concentrations (0, 0.6, 3 and 6 μg g^?1) over 8 weeks. Cellulose decomposition in soil was also studied in laboratory experiments with the herbicide which was either incorporated in soil or sprayed onto calico squares which were buried in soil. The mycelial dry weight of six fungal species under the effect of the herbicide was also examined. Fluazifop-butyl had no significant effect on total fungal propagule populations at 0.6 μg g^?1. At 3 and 6 μg g^?1, it caused temporary reduction in fungal populations observed after 1 and 2-wk of incubation. The herbicide had no significant effect on OZ uptake. The decay of calico buried in herbicide-treated soil was generally stimulated, while the decomposition of herbicide-treated calico, buried in untreated soil, was temporary delayed. The mycelial dry weight yields of Aspergillus favus (at 2 and 12 μg mL^?1 of fluazifop-butyl) and Cunninghamella echinulata (at 12 μg mL^?1) were significantly increased. At 24 μg mL^?1 the mycelial dry weight of A. flavus and Alternaria alternata was significantly reduced.     

Starch Damage and Pasting Properties of Rice Flours Produced by Dry Jet Grinding

Milling method and particle size affect some properties of rice flour. To prepare ultra‐fine rice flour of <30 μm, hammer and dry jet grinding methods were examined and the effect of particle size on starch damage and pasting properties of the flour were elucidated. A jet mill could make finer flour (<10 μm mean size) with a narrower particle size distribution than a hammer mill could. Starch damage increased dramatically at a mean size of <10 μm. Particles of a similar size (<60 μm) had different levels of starch damage between mills. Not only the particle size, but also the milling method affected the level of damaged starch. Flour samples of ≥45 μm mean size had similar viscosity curves, but samples of <20 μm had different curves. Peak viscosity and final viscosity decreased sharply at <10 μm. Setback viscosity for particles of 3 μm from both brown rice and white rice were higher than the peak viscosity. Stability to heat and shearing stress were decreased for <20 μm flours as the breakdown viscosities decreased. Starch damage and pasting properties of flour ground from the nonwaxy japonica cultivar Koshihikari changed dramatically at a mean size of <10 μm.